Women with an especially deadly form of breast cancer have been given new hope by the discovery of a molecule that helps their tumours grow and spread.

The molecule, known as alpha v beta 6, could be used both to identify at-risk patients and develop new treatments, say scientists.

A study found high levels of alpha v beta 6 in 40% of tumours in women with HER2 positive breast cancer, a form of the disease that does not respond to conventional hormone therapy.

These patients were twice as likely to die within five years of diagnosis as those with low levels of the molecule.

In experiments on mice with the same type of breast cancer, scientists used an antibody drug to block activity of alpha v beta 6.

Combining the antibody with the drug Herceptin, which targets the cancer-driving HER2 protein, completely eradicated the animals' tumours after six weeks of treatment.

Researcher Dr Kate Moore, from Queen Mary University of London's Barts Cancer Institute, said: "We found that simultaneously targeting alpha v beta 6 and HER2 in mice with tumours grown from human breast cancer cells greatly improved the effectiveness of Herceptin - even eliminating tumours that did not respond to Herceptin alone, which could have the potential to improve treatments for patients with these highly aggressive cancers."

Using the antibody on its own reduced the size of tumours in the mice by 94.8%. In comparison, treatment with Herceptin alone led to a 77.8% reduction.

Up to 70% of women with HER2-positive breast cancer either do not respond to Herceptin or develop resistance to the drug, leaving up to 7,000 women a year in the UK with limited treatment options.

Dr John Marshall, who led the Barts Cancer Institute team with funding from the Breast Cancer Campaign charity and Medical Research Council, said: "The results of this pre-clinical study suggest that targeting the alpha v beta 6 molecule may enhance the effectiveness of Herceptin - and that a combination treatment could be effective for patients where Herceptin alone has not worked.

" High alpha v beta 6 levels could be tested for in routine biopsies to identify which women are at a high risk of metastasis (cancer spread), ensuring these women can receive personalised treatment, improving their chances of survival."

The research is published online in the Journal of the National Cancer Institute.

Baroness Delyth Morgan, the chief executive of Breast Cancer Campaign, said: "Despite great advances in the past 20 years, five-year breast cancer survival in the UK is worse than the European average.

"There is a desperate need for drugs which work in new ways to give the thousands of women diagnosed with HER2-positive breast cancer the best possible chances of surviving the disease. This study could pave the way for new treatments and bring us closer to our goal of preventing half of the deaths from breast cancer by 2025, through improved and personalised treatments."

The charity has just launched a new campaign, "spread the word to stop the spread", highlighting the fact that 12,000 women still die from breast cancer each year in the UK.